It is widely believed that cognitive uncertainty-doubt and internal conflict-plays a crucial role in promoting and directing learning and cognitive development. Unfortunately, however, the study of learning and cognitive development has relied on procedures that tend to mask individuals' awareness of their own uncertainty. Recent studies by ourselves and others have indicated, however, that the new testing methods can unveil judgment uncertainty when it is present. Application of these procedures suggest that judgment uncertainty is much more prevalent than previously assumed. Research completed under the existing grant was inspired by the recognition that given the likely importance of uncertainty as a dynamic force in cognitive development, we need to begin a reinvestigation of cognition using these new methods with an eye to charting the course of judgment certainty over the course of concept development. The present request for a continuation will permit completion of a long-term microgenetic assessment of the role of cognitive uncertainty in cognitive development. In particular, the project will examine the hypotheses that (1) transitions in learning and cognitive development proceed through a sequence of increasing and then decreasing uncertainty; (2) children in "transition"-that is, in a state of instability and uncertainty-are more likely to show spontaneous (i.e., untrained) development, and are more likely to respond to direct training or learning experiences, and (3) cognitive development is hastened when Children are made aware of their own uncertainty. Our theory proposes that when one recognizes one's own uncertainty it motivates efforts to resolve the doubt and conflicts. Internal reflection, often in conjunction with increased vigilance and the purposive search for relevant information, increases the likelihood that the individual will quickly find a personally satisfying resolution to their uncertainty that is simultaneously an advancement in their level of knowledge or skill.